The present invention relates to x-ray system measurements, and, more particularly, to radiation exposure or Air-Kerma prediction for radiographic x-ray exposures.
Extensive scientific work has been done in the x-ray field measuring x-ray tube output in terms of radiation exposure (expressed in units of Roentgen) and Air-Kerma (expressed in units of Gray). This quantity is also known as the absorbed x-ray dose in air. Kerma stands for Kinetic Energy Released in the Medium and quantifies the amount of energy from the x-ray beam absorbed per unit mass. Radiation exposure is related to energy absorbed specifically in a given volume of air.
From a regulatory point of view, absorbed radiation dose or radiation exposure to the patient is often the key parameter of concern. Today, the general policy is to protect patients from unreasonable radiation dose, while still allowing the radiologist to obtain an image of acceptable quality. To control the level of exposure, new regulations, some already in effect in certain countries, require dose area product levels during an x-ray procedure to be reported. Furthermore, with ever-increasing concern for the quality of care, there is increased interest in regulatory evaluation of x-ray equipment.
Various methods have evolved to measure, predict, and control this x-ray quantity. In a current system, the xe2x80x9cDose Area Productxe2x80x9d (reporting either radiation exposure or Air-Kerma) is measured directly with an ion chamber positioned in front of the collimator at the output of the x-ray tube. Alternatively, this quantity can also be predicted by monitoring x-ray techniques used in an exposure and, after calibrating radiation exposure measurements, then calculating and reporting the value.
Unfortunately, use of an ion chamber probe degrades the performance of the x-ray system, as the probe acts as an unnecessary attenuator in the x-ray beam. Additionally, the second method requires extensive calibrations that are not practical for many systems.
Therefore, due to the increasing demands in x-ray system performance, reduced system calibration needs, and increasing regulatory control, a new, predictive, non-invasive method for gathering reliable, non-falsifiable patient entrance exposure information, is desired.
In accordance with one preferred embodiment, a system is provided that predicts radiation exposure/Air-Kerma at a predefined patient entrance plane and the radiation exposure/Air-Kerma area product during a radiographic x-ray exposure. With this system, the need for the ion chamber and/or extensive system calibration are eliminated, as the radiation exposure/Air-Kerma levels are predicted directly from the x-ray exposure parameters. Additionally, this system satisfies known regulatory requirements in radiographic x-ray exposures. Additionally, the present invention satisfies known regulatory requirements in radiographic x-ray exposures.
In accordance with another preferred embodiment, a method is provided to predict the radiation exposure of Air-Kerma for an arbitrary radiographic x-ray exposure by providing input variables to identify the spectral characteristics of the x-ray beam, providing a neural net which has been trained to calculate the exposure or Air-Kerma value, and by scaling the neural net output by the calibrated tube efficiency, the actual mAs and the actual source-to-object distance.
The preferred embodiments provide a radiation exposure/Air-Kerma prediction at a predefined patient entrance plane; and further to provide a radiation exposure/Air-Kerma area product prediction during a radiographic x-ray exposure. This makes it possible to eliminate the use of a measuring probe that otherwise would have to be installed on the x-ray system, providing the advantages of reducing system cost and simplifying system packaging and power supplies. This also makes it possible to significantly reduce system calibrations needed for this reported measurement.